Many computers currently sold include a wired network card for connecting to a computer network using a cable and a wireless network card for connecting to a computer network wirelessly. Typically, a wired network card connects directly either to a modem or to a local area network (LAN) using a network cable. A wireless network card generally connects to a wireless LAN using a wireless protocol such as those defined by IEEE 802.11b/g/n.
Additionally, many modern operating systems enable network bridging, a feature that allows network cards within the same computer to communicate directly with one another so that all packets received on one network interface are transmitted on the second network interface. The prevalence of computers containing both wired and wireless network cards, together with the ease of enabling network bridging on the computers increases the potential for a user to inadvertently create a network loop.
A network loop is formed, for example, when a computer with network bridging enabled has a wired network card and a wireless network card connected to the same LAN. In this configuration, if a broadcast packet is sent to one of the computer's network cards, it will be forwarded to the other network card and sent to the network again. In this way, the broadcast packet can circulate around the network repeatedly, resulting in wasted bandwidth and potentially consuming CPU resources and delaying other network communications.
Currently known methods of detecting loops in a wired LAN include a spanning tree protocol, such as the protocol defined by IEEE 802.1D. However, computers with bridging enabled typically do not respond to packets sent out using spanning tree protocol, and not all access points support the spanning tree protocol. Thus, spanning tree protocol does not provide a comprehensive solution for identifying network loops caused by a device connecting to a network using both a wired and wireless interface.